The present invention broadly relates to a new and improved safety beading or ledge which may be disposed along the shock-absorbing edges or closing edges of an automatically movable or driverless contrivance, and more specifically, to a safety beading arranged along the shock-absorbing edges of automatic vehicles or along the closing edges of automatically closing doors, wherein the safety beading comprises an electric switching arrangement which includes contact elements which are carried by elastically deformable insulating bodies.
Such safety beadings or ledge serve the purpose in automatically operating devices, for example in driverless transport vehicles, for factory or warehouse floor transportation or in automatic vehicle doors, to switch-off the drive upon contact with an obstacle, or to initiate a braking action.
Switching beadings or ledges, contact mats and similar arrangements are known which in principle consist of two electric conductors held apart elastically, in the form of metal bands, wires and the like, which upon impact with an obstacle are pressed together, thus to cause a short circuit-like increase in the current of a control circuit.
In such a safety device, as shown in German Published Pat. No. 2,719,438 for the closing edges of automatically operated vehicle doors, there is provided a signal generator which extends over the whole length of the edge, and which comprises two ribbon-like electric conductors, which in the inoperative condition are kept apart at a certain distance in an elastically deformable insulating body. The conductors are provided in the region of one end with a voltage source and with a drive control device, and in the region of the other end they are connected by way of a measuring resistance with one another, whereby a no-load or closed circuit is formed. If the signal generator is pressed together anywhere along its length the two ribbon-like electric conductors come into contact, which results in a change in the resistance of the no-load or closed-current circuit, whereupon, for example, the drive vehicle door is stopped by means of a relay.
In the safety device described above it can happen that because of the presence of corrosion or dirt no contact is made, so that the drive to the vehicle door is not switched-off. Since the switching device which switches-off the drive is activated as a result of an increase in the no-load or closed-circuit current, it is possible that, for example, in the case of a defective relay, switching-off also fails to take place.